Signal processing apparatus

ABSTRACT

A signal processing apparatus comprising a plurality of video signal correlation detecting means for detecting the values of video signal correlations in a plurality of ways with respect to the displayed picture, and intermediate value selecting means for selecting an intermediate value among the detected values of the plurality of video signal correlations, whereby a changing video signal is processed by utilizing a correlation of a proper way.

TECHNICAL FIELD

The present invention relates to a video signal processing apparatusutilizing the principle of signal correlation to separate the luminanceand chrominance signals.

BACKGROUND ART

In prior art video signal separating systems, it is known to utilizehorizontal correlation, vertical correlation and time (frame)correlation of both the luminance signal Y and a carrier chrominancesignal (chroma signal) C to separate them. Correlation is meant how thesignals change along a line, from line to line, or from frame to frame,respectively. Known Y/C separating circuits utilizing the aboverespective correlations will hereinafter be described with reference toFIGS. 8 to 10.

FIG. 8A illustrates a horizontal correlation type Y/C separatingcircuit. Referring to FIG. 8A, a video signal applied to an inputterminal 1 is supplied in common to a low pass filter 2Y and a bandpassfilter 2C. From an output of the low pass filter 2Y, a luminance signalY_(H) is supplied to an output terminal 3Y, whereas from an output ofthe bandpass filter 2C, a chroma signal C_(H) is supplied to an outputterminal 3C.

FIG. 8B illustrates a vertical correlation type Y/C separating circuit.Referring to FIG. 8B, a video signal applied to an input terminal 1 issupplied in common to a 1H delay line 4, an adder 5Y and a subtracter5C. The output from the 1H delay line 4 is supplied in common to theadder 5Y and the subtracter 5C. As a result, a luminance signal Y_(V)from the adder 5Y is supplied to an output terminal 6Y and a chromasignal C_(V) from the subtracter 5C is supplied to an output terminal6C.

FIG. 8C illustrates a frame correlation type Y/C separating circuit.Referring to FIG. 8C, a video signal applied to an input terminal 1 issupplied in common to an adder 8Y, a subtracter 8C and a frame memory 7which constitutes a one frame delay line. The output of the frame memory7 is supplied to the adder 8Y and the subtracter 8C. As a result, aluminance signal Y_(F) from the adder 8Y is supplied to an outputterminal 9Y and a chroma signal C_(F) from the subtracter 8C is suppliedto an output terminal 9C.

While the frame memory 7 is inherently designed to process a digitizedsignal, it is arranged in the circuit of the invention so as to processan analog signal for the sake of simplicity. Therefore, an A/D(analog-to-digital) converter at the input side thereof and a D/A(digital-to-analog) converter at the output side thereof are not shownbut are understood to be included.

FIGS. 9A to 9C illustrate frequency vs. amplitude characteristics of theY/C separating circuits shown in FIGS. 8A to 8C, respectively.

In FIG. 9A, a bold solid curve indicates the pass band characteristic ofthe low pass filter 2Y and a dashed curve the pass band characteristicof the bandpass filter 2C. In FIG. 8A, the low pass filter 2Y can bereplaced by a subcarrier trap. In this case, the pass bandcharacteristic is indicated as both bold and fine solid curves in FIG.9A.

The vertical correlation type Y/C separating circuit of FIG. 8Bconstitutes a known comb filter. The pass band characteristic of thiscomb filter relative to the luminance signal Y_(V) is made, as shown bya solid curve in FIG. 9B, to have the maximum attenuation degree at asubcarrier frequency fsc and respective points spaced apart therefrom bythe distance of some integer times the horizontal frequency f_(H) andthe minimum attenuation degree at each of intermediate points betweenthese points, i.e. at each of the points spaced apart from thesubcarrier frequency fsc by the distance of an odd number times 1/2 ofthe horizontal frequency f_(H) : (2n+1) f_(H) /2. On the other hand, thepass band characteristic thereof relative to the chroma signal C_(V) ismade, as shown by a dashed curve in FIG. 9B, to have a minimumattenuation degree at the subcarrier frequency fsc and respective pointsspaced apart therefrom by the distance of some integer times thehorizontal frequency f_(H) and a maximum attenuation degree at each ofthe points spaced apart from the subcarrier frequency fsc by thedistance of an odd number times the horizontal frequency f_(H), i.e.(2n+1) f_(H) /2.

The reason for this is that by the known technique of frequencyinterleaving, as shown by dashed line in FIG. 10A, the spectrums of thechroma signal C are located between the spectrums of the luminancesignal Y shown by a solid line in the same figure.

The frame correlation type Y/C separating circuit of FIG. 8C forms aknown comb filter. The pass band characteristic of this comb filterrelative to the luminance signal Y_(F) is made, as shown by a solidcurve in FIG. 9C, to have the maximum attenuation degree at thesubcarrier frequency fsc and respective points spaced apart by thedistance of some integer times the frame frequency f_(F) (=f_(V) /2) andthe minimum attenuation degree at each of the intermediate pointsbetween these points, that is, points spaced apart from the subcarrierfrequency fsc by the distance of an odd number times 1/2 of the framefrequency f_(F), i.e. (2n+1) f_(F) /2. On the other hand, the pass bandcharacteristic thereof relative to the chroma signal C_(F) is made, asshown by a dashed line in FIG. 9C, to have the minimum attenuationdegree at the subcarrier frequency fsc and respective points spacedapart therefrom by the distance of some integer times the framefrequency f_(F) and the maximum attenuation degree at respective pointsspaced apart from the subcarrier frequency fsc by the distance of oddtimes of 1/2 of the frame frequency f_(F), i.e. (2n+1) f_(F) /2.

The reason for this will be understood as follows. As shown in FIG. 10B,which is a partially enlarged view of FIG. 10A, by the known techniqueof frequency interleaving, a side band wave (shown by an open circle) ofthe vertical frequency f_(V) accompanied with an odd higher harmonicwave of the horizontal frequency f_(H) and a side band wave (shown by asolid circle) of the vertical frequency f_(V) accompanied with an evenhigher harmonic wave are spaced apart from each other by a distance ofthe frame frequency f_(F) =f_(V) /2. Then, the subcarrier frequency fscand the side band wave of the vertical frequency f_(V) accompaniedtherewith are located between the frequency intervals of the framefrequency f_(F).

However, these known Y/C separating apparatus, individually utilizingvarious correlations, cause the quality of the reproduced picture to bedeteriorated at the places when no correlation exists.

When horizontal correlation is utilized, the deterioration of thequality of picture, such as the deterioration of a frequencycharacteristic and the occurrence of crosstalk, occurs on the picture atits right and left side edges of the longitudinal stripes as shown inFIG. 11A when the levels of the luminance signal Y and the chroma signalC are changed abruptly in the horizontal direction.

When vertical correlation is utilized, the deterioration of the qualityof picture, such as the occurrence of crosstalk and the appearance ofdots of the subcarrier, occurs on the picture at the top and bottomedges of the horizontal stripes as shown in FIG. 11B when the levels ofthe luminance signal Y and the chroma signal C are abruptly changed inthe vertical direction.

When frame correlation is utilized, as shown in FIGS. 11C1 to 11C3,crosstalk occurs in part or wholly in the peripheral edge of the picturein relation to the direction in which a figure in the picture is movedin the directions shown by arrows and also the quality of picture isconsiderably deteriorated, such as multiple-line interference or thelike when the peripheral edge of the figure is doubled or tripled.

In order to solve such problems, it may be proposed to switch theseparated outputs in response to the moving amount of the pictureelement at a proper timing. In this case, the signal processingapparatus needs a moving picture element detecting section which wouldcause the arrangement of the apparatus to be large in size andcomplicated.

DISCLOSURE OF INVENTION

It is therefore an object of this invention to provide a video signalluminance and chrominance signal separating apparatus which can improvethe quality of a reproduced picture without requiring a moving pictureelement detecting section.

This is accomplished in the present invention by providing a signalprocessing apparatus comprising a plurality of video signal correlationdetecting means for detecting the values of video signal correlations ina plurality of directions with respect to the displayed picture, andintermediate value selecting means for selecting an intermediate valueamong the detected values of the plurality of video signal correlations,whereby a changing video signal is processed by utilizing a correlationof a proper direction.

According to the present invention, the changing video signal can beprocessed by the correlation of the proper direction without detecting amoving image of the displayed picture, so that the quality of thereproduced picture can be improved.

The foregoing and other objectives, features and advantages of theinvention will be more readily understood upon consideration of thefollowing detailed description of certain preferred embodiments of theinvention, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a circuit arrangement of oneembodiment in which a signal processing apparatus of the invention isapplied to a Y/C separation;

FIGS. 2 and 3 are respectively block diagrams showing the arrangement ofmain portions of the embodiment in FIG. 1;

FIG. 4 is a block diagram showing a circuit arrangement of anotherembodiment in which the present invention is applied to the Y/Cseparation;

FIG. 5 is a block diagram showing an arrangement of a main portion ofthe embodiment shown in FIG. 4;

FIG. 6 and FIGS. 7A and 7B are respectively block diagrams showingarrangements of further embodiments in which the present invention isapplied to a noise elimination;

FIGS. 8A to 8C are respectively block diagrams showing circuitarrangements of prior art Y/C separating circuits;

FIGS. 9A to 9C are respectively graphs showing frequency vs. amplitudecharacteristics of the prior art Y/C separating circuits in FIGS. 8A to8C;

FIGS. 10A and 10B are spectral diagrams of a video signal used toexplain the present invention; and

FIGS. 11A to 11C3 are respectively conceptual diagrams showingreproduced pictures of the prior art Y/C separating circuits.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of a signal processing apparatus according to the presentinvention will hereinafter be described with reference to FIGS. 1 and 2where this embodiment is applied to the process of Y/C separating.

FIG. 1 illustrates a circuit arrangement of the embodiment of theinvention. In FIG. 1, like parts corresponding to those of FIG. 8 aremarked with the same references and therefore they are not furtherdescribed.

Referring to FIG. 1, there are provided a horizontal correlation typeY/C separating circuit H Corr, a vertical correlation type Y/Cseparating circuit V Corr and a frame correlation type Y/C separatingcircuit F Corr which are constructed as shown in FIGS. 8A, 8B and 8C,respectively. A video signal applied to an input terminal 11 is suppliedin common to these Y/C separating circuits H Corr, V Corr and F Corr.Further, there are provided intermediate value selecting circuits 12Yand 12C.

The intermediate value selecting circuit 12Y is supplied with outputsignals Y_(H), Y_(V) and Y_(F) of the low pass filter 2Y and both adders5Y and 8Y, respectively. The other intermediate value selecting circuit12C is supplied with output signals C_(H), C_(V) and C_(F) of the lowpass filter 2C and both subtracters 5C and 8C, respectively.

FIG. 2 illustrates an example of the circuit arrangement of each of theintermediate value selecting circuits 12Y and 12C. Input terminals 21H,21V and 21F, respectively, receive the outputs of the Y/C separatingcircuits H Corr, V Corr and F Corr of FIG. 1 at input terminals 21H,21V, and 21F, respectively. Maximum value selecting circuits 22, 23 and24 are connected such that an input signal from the input terminal 21His supplied to the third and first maximum value selecting circuits 24and 22, respectively, an input signal from the input terminal 21V issupplied to the first and second maximum value selecting circuits 22 and23, respectively, and an input signal from the input terminal 21F issupplied to the second and third maximum value selecting circuits 23 and24, respectively. The outputs A, B, C, respectively, of the first tothird maximum value selecting circuits 22 to 24 are all supplied to aminimum value selecting circuit 25 and the output from the minimum valueselecting circuit 25 is delivered to a terminal 13.

The operation of the intermediate value selecting circuit of FIG. 2 willbe described next.

Let it now be assumed that the amplitudes of the luminance signalsY_(H), Y_(V) and Y_(F) supplied from the respective Y/C separatingcircuits H Corr, V Corr and F Corr of FIG. 1 to the respective inputterminals 21H, 21V and 21F of the intermediate value selecting circuitof FIG. 2 satisfy the condition of, for example, Y_(H) >Y_(V) >Y_(F).

Then, the luminance signals Y_(H) and Y_(V) are supplied to the firstmaximum value selecting circuit 22, so that the luminance signal Y_(H),which has an amplitude larger than that of the luminance signal Y_(V),appears at the output A of the circuit 22. The second maximum valueselecting circuit 23 is supplied with the luminance signals Y_(V) andY_(F), so that the luminance signal Y_(V), having an amplitude largerthan that of the luminance signal Y_(F), appears at the output B of thecircuit 23. Further, the third maximum value selecting circuit 24 issupplied with the luminance signals Y_(F) and Y_(H), so that theluminance signal Y_(H), having an amplitude larger than that of theluminance signal Y_(F), appears at the output C of the circuit 24.

Since the minimum value selecting circuit 25 is supplied with theoutputs A, B and C, i.e. the luminance signals Y_(H), Y_(V) and Y_(H)from the maximum value selecting circuits 22 to 24, it generates theluminance signal Y_(V), which has the smallest amplitude. Since thecondition of Y_(H) >Y_(V) >Y_(F) is satisfied, the intermediate valueY_(V) is thus selected by the circuit arrangement of FIG. 2.

If the condition of three luminance signals Y_(H), Y_(V) and Y_(F) isdifferent from that described above, the intermediate value selectingcircuit of FIG. 2 operates to produce outputs as shown in the table 1below. Under all conditions the intermediate value among three luminancesignals Y_(H), Y_(V) and Y_(F) is selected by the intermediate valueselecting circuit.

                  TABLE 1                                                         ______________________________________                                        Case         A     B         C   Output (13)                                  ______________________________________                                        Y.sub.H > Y.sub.V > Y.sub.F                                                                Y.sub.H                                                                             Y.sub.V   Y.sub.H                                                                           Y.sub.V                                      Y.sub.F > Y.sub.V > Y.sub.H                                                                Y.sub.V                                                                             Y.sub.F   Y.sub.F                                                                           Y.sub.V                                      Y.sub.V > Y.sub.H > Y.sub.F                                                                Y.sub.V                                                                             Y.sub.V   Y.sub.H                                                                           Y.sub.H                                      Y.sub.F > Y.sub.H > Y.sub.V                                                                Y.sub.H                                                                             Y.sub.F   Y.sub.F                                                                           Y.sub.H                                      Y.sub.H > Y.sub.F > Y.sub.V                                                                Y.sub.H                                                                             Y.sub.F   Y.sub.H                                                                           Y.sub.F                                      Y.sub.V > Y.sub.F > Y.sub.H                                                                Y.sub.V                                                                             Y.sub.V   Y.sub.F                                                                           Y.sub.F                                      ______________________________________                                    

If the amplitudes of two input signals applied to each of the maximumvalue selecting circuits 22 to 24 are equal to each other, either one ofthem may be selected. In this case, the intermediate value selectingcircuit of FIG. 2 never selects a third input signal and therelationships indicated in the table 1 are established.

The intermediate value selecting circuit 12C, which is also illustratedin FIG. 2, is operated relative to the chroma signals C_(H), C_(V) andC_(F) in the same way as described above for the circuit 12Y.

The operation of the embodiment shown in FIG. 1 will now be described.The picture shown in FIG. 11A has the correlation in the verticaldirection, i.e. the displayed image is relatively constant in thevertical direction. Conversely, the picture shown in FIG. 11B has thecorrelation in the horizontal direction. Further, correlations in theframe (time) directions appear in the still pictures shown in FIGS. 11C1to 11C3, i.e. some part of the picture remains relatively constant fromframe to frame.

When the picture has a correlation in any of the horizontal, verticaland time directions, there is a large probability that of the outputsfrom the Y/C separating circuits H Corr, V Corr and F Corr of FIG. 1,the output corresponding to the direction having the correlation willbecome an intermediate value while the output corresponding to thedirection having no correlation becomes either larger or smaller thanthe output corresponding to the correlation. For this reason, accordingto the embodiment of FIG. 1, the intermediate value selecting circuit12Y selects the luminance signal Y corresponding to the way in which thepicture has correlation. At the same time, the other intermediate valueselecting circuit 12C selects the chroma signal C corresponding to theway in which the picture has the correlation. Thus, the optimum Y/Cseparation for various pictures which are being changed at any time iscarried out, so that the quality of the reproduced picture is improved.

Alternatively, as shown in FIG. 3, the intermediate value selectingcircuits 12Y or 12C can be constructed by replacing the maximum valueselecting circuits 22, 23 and 24 of FIG. 2 with minimum value selectingcircuits 26, 27 and 28 and by replacing the minimum value selectingcircuit 25 of FIG. 2 with a maximum value selecting circuit 29. Theoutputs D, E and F correspond to the outputs of the circuits 26, 27 and28, respectively.

Relative to the level relationships of the three luminance signalsY_(H), Y_(V) and Y_(F), the intermediate value selecting circuit of FIG.3 is operated in accordance with table 2 below. This intermediate valueselecting circuit is operated in the same way relative to the chromasignals C_(H), C_(V) and C_(F).

                  TABLE 2                                                         ______________________________________                                        Case         A     B         C   Output (13)                                  ______________________________________                                        Y.sub.H > Y.sub.V > Y.sub.F                                                                Y.sub.V                                                                             Y.sub.F   Y.sub.F                                                                           Y.sub.V                                      Y.sub.F > Y.sub.V > Y.sub.H                                                                Y.sub.H                                                                             Y.sub.V   Y.sub.H                                                                           Y.sub.V                                      Y.sub.V > Y.sub.H > Y.sub.F                                                                Y.sub.H                                                                             Y.sub.F   Y.sub.F                                                                           Y.sub.H                                      Y.sub.F > Y.sub.H > Y.sub.V                                                                Y.sub.V                                                                             Y.sub.V   Y.sub.H                                                                           Y.sub.H                                      Y.sub.H > Y.sub.F > Y.sub.V                                                                Y.sub.V                                                                             Y.sub.V   Y.sub.F                                                                           Y.sub.F                                      Y.sub.V > Y.sub.F > Y.sub.H                                                                Y.sub.H                                                                             Y.sub.F   Y.sub.H                                                                           Y.sub.F                                      ______________________________________                                    

When the levels of two input signals applied to the minimum valueselecting circuits 26 to 28 are equal to each other, the intermediatevalue selecting circuit of FIG. 3 never selects a third input and therelationships indicated on the table 2 are established.

Other embodiments of the signal processing apparatus according to thepresent invention will now be described with reference to FIGS. 4 and 5in which this embodiment is applied to the Y/C separation.

FIG. 4 illustrates a circuit arrangement of another embodiment of thesignal processing apparatus according to this invention. In FIG. 4, likeparts corresponding to those of FIG. 1 are marked with the samereference numerals and their description will be omitted.

Referring to FIG. 4, a transversal filter 31 is provided to include fourunit delay lines 32₁, 32₂, 32₃ and 32₄ connected in series and aweighting adding circuit 33. The input side of the first unit delay line32₁, each of junctions between adjacent ones of the first to fourth unitdelay lines 32₁ to 32₄ and the output side of the fourth unit delay line32₄ are connected to the weighting adding circuit 33. The transversalfilter 31 is equivalent to the horizontal correlation type Y/Cseparating circuit H Corr which is formed of the low pass filter 2Y andthe bandpass filter 2C as shown in FIG. 1 and is operated at a clockfrequency of, for example, 4 fsc. Each of the unit delay lines 32₁ to32₄ has a delay time D.

In the transversal filter 31, the output from the fourth unit delay line32₄ is supplied to a first memory 34. The output from the first memory34 is supplied in common to an adder 35Y and a subtracter 35C, whereasan output developed at the junction between the second and third unitdelay lines 32₂ and 32₃ is supplied in common to the adder 35Y and thesubtracter 35C. The delay time of the first memory 34 is selected to be1H-2D. This memory 34 and the third and fourth unit delay line 32₃ and32₄ of the transversal filter 31 constitute a line memory whose delaytime is selected as 1H. The line memory, the adder 35Y and thesubtracter 35C constitute the vertical correlation type Y/C separatingcircuit V Corr.

The output from the first memory 34 is supplied to a second memory 37and the output of this second memory 37 is supplied in common to asecond adder 38Y and a second subtracter 38C. The output developed atthe junction between the second and third unit delay lines 32₂ and 32₃of the transversal filter 31 is supplied in common to the adder 38Y andthe subtracter 38C. The second memory 37 has a delay time of 1F-1H. Thesecond memory 37, the first memory 34 and the third and fourth fourthunit delay lines 32₃ and 32₄ of the transversal filter 31 constitute aframe memory of which the delay time is selected to be 1F (one frameperiod). This frame memory, the second adder 38Y and the secondsubtracter 38C constitute the frame correlation type Y/C separatingcircuit F Corr.

The intermediate value selecting circuit 12Y is supplied with theoutputs Y_(H), Y_(V) and Y_(F) of the transversal filter 31 and both theadders 35Y and 38Y, respectively. The other intermediate value selectingcircuit 12C is supplied with the outputs C_(H), C_(V) and C_(F) of thetransversal filter 31 and both the subtracters 35C and 38C,respectively.

FIG. 5 illustrates an example of the circuit arrangement of each of theintermediate value selecting circuits 12Y and 12C according to thisembodiment. Input signals applied to input terminals 21H, 21V and 21Fare supplied in common to a maximum value selecting circuit 41, aminimum value selecting circuit 42 and an adder 43. Outputs G and H fromthe maximum value selecting circuit 41 and the minimum value selectingcircuit 42, respectively, are supplied to a second adder 44. The outputfrom the first adder 43 is supplied to a subtracter 45 and an output Jfrom the second adder 44 is supplied to the subtracter 45 in which theoutput J is subtracted from the output of the adder 43.

Relative to 6 levels of relationships among three luminance signalsY_(H), Y_(V) and Y_(F), the intermediate value selecting circuit of FIG.5 is operated in accordance with the following table 3. Thisintermediate value selecting circuit is operated in the same wayrelative to the chroma signals C_(H), C_(V) and C_(F).

                  TABLE 3                                                         ______________________________________                                        Case         G     H       J      Output (13)                                 ______________________________________                                        Y.sub.H > Y.sub.V > Y.sub.F                                                                Y.sub.H                                                                             Y.sub.F Y.sub.H + Y.sub.F                                                                    Y.sub.V                                     Y.sub.F > Y.sub.V > Y.sub.H                                                                Y.sub.F                                                                             Y.sub.H Y.sub.H + Y.sub.F                                                                    Y.sub.V                                     Y.sub.V > Y.sub.H > Y.sub.F                                                                Y.sub.V                                                                             Y.sub.F Y.sub.V + Y.sub.F                                                                    Y.sub.H                                     Y.sub.F > Y.sub.H > Y.sub.V                                                                Y.sub.F                                                                             Y.sub.V Y.sub.V + Y.sub.F                                                                    Y.sub.H                                     Y.sub.H > Y.sub.F > Y.sub.V                                                                Y.sub.H                                                                             Y.sub.V Y.sub.H + Y.sub.V                                                                    Y.sub.F                                     Y.sub.V > Y.sub.F > Y.sub.H                                                                Y.sub.V                                                                             Y.sub.H Y.sub.H + Y.sub.V                                                                    Y.sub.F                                     ______________________________________                                    

Even when two out of three input signals are equal to each other inlevel, the relationships in the table 3 are established.

The intermediate value selecting circuit shown in FIG. 5 together withthe horizontal correlation type and frame correlation type Y/Cseparating circuits H Corr and F Corr of FIG. 4 are formed of digitalcircuits. This is also true for the intermediate value selectingcircuits which are constructed fundamentally as shown in FIGS. 2 and 3.

In this way, the embodiment of FIG. 4 is operated in the same way asthat of the embodiment of FIG. 1, so that for a picture changing at anytime, the luminance signal Y and the chroma signal C in the way in whichthe picture has correlation are selected to thereby carry out theoptimum Y/C separation, thus improving the quality of a reproducedpicture.

A further embodiment of the signal processing apparatus according to thepresent invention will be described with reference to FIG. 6 in whichthis embodiment is applied to a noise eliminating circuit. A noiseeliminating circuit 50 comprises horizontal, vertical and framecorrelation detecting circuits 51, 52 and 53 and an intermediate valueselecting circuit 54 which is supplied with the outputs from thesecorrelation detecting circuits 51 to 53. The correlation detectingcircuits 51 to 53 correspond to the signal separating circuits describedabove and generate signals of the same kind as that of theaforementioned luminance signals Y_(H), Y_(V) and Y_(F). Further, theintermediate value selecting circuit 54 is constructed as shown in FIG.2, FIG. 3 or FIG. 5.

In the embodiment shown in FIG. 1 or FIG. 4, for one of the luminancesignal Y and the chroma signal C, the other signal to be separated maybe noise. Further, since the video signal has correlation and the noisehas no correlation, it will be easily understood that the noiseeliminating circuit of this embodiment is operated in the same way asthat of the Y/C separating circuit shown in FIG. 1 or FIG. 4 to therebyseparate the video signal and the noise. In other words, it will beeasily understood that the noise can be eliminated from the videosignal.

As shown in FIG. 7A, a noise eliminating apparatus of a recursive typemay be comprised of the noise eliminating circuit 50 of the embodimentshown in FIG. 6 and a subtracter 55.

Further, as shown in FIG. 7B, a first subtracter 56 is connected to theinput side of the noise eliminating circuit 50 and a second subtracter57 is connected to the output side of the circuit 50. The secondsubtracter 57 subtracts the output signal (which hardly contains anynoise) of the noise eliminating circuit 50 from the input signal (whichdoes contain the noise) to the noise eliminating circuit 50 to therebyseparate the noise component from the video signal. Then, the noisecomponent separated, which is obtained from the output of the subtracter57, is subtracted by the subtracter 56 connected to the input side ofthe noise eliminating circuit 50 to thereby eliminate the noisecontained in the input signal applied to the noise eliminating circuit50. Thus, the S/N (signal-to-noise) ratio of the output signal can beimproved even more.

The noise eliminating apparatus to which the present invention isapplied is not limited to the above mentioned embodiment but manymodifications and variations could be effected by those skilled in theart.

According to the present invention, as set forth above in detail, thevideo signal correlations in a plurality of ways are detected and theintermediate value of these correlation detected values is selected, sothat without the necessity of detecting a moving picture element, thecorrelation of the optimum way can be utilized for the picture changingat any time. Accordingly, it is possible to obtain a signal separatingapparatus which can improve the quality of the reproduced picture.

What is claimed is:
 1. A circuit for separating the luminance andchrominance signals from a video signal which is changing with time inone or more ways relative to a picture displayed from the video signal,the circuit comprising:a plurality of luminance and chrominance signalseparating means for separating said luminance and chrominance signalsfrom said video signal using correlations in a plurality of said ways;and intermediate value selecting means for selecting the luminance andchrominance signals having intermediate values among the separatedsignals.
 2. A circuit for separating the luminance and chrominancesignals from a video signal as recited in claim 1 whereinthe luminanceand chrominance signal separating means include a low pass filter forseparating the luminance signal and a bandpass filter for separating thechrominance signal, whereby horizontal correlation is utilized for theseparation.
 3. A circuit for separating the luminance and chrominancesignals from a video signal as recited in claim 1 whereinthe luminanceand chrominance signal separating means include a delay circuit having adelay period of one horizontal line period, an adder, a subtracter, andwherein the video signal is supplied in common to the adder, thesubtracter, and the delay circuit and the output of the delay circuit issupplied in common to the adder and the subtracter whereby the luminancesignal is derived at the output of the adder and the chrominance signalis derived at the output of the subtracter based on verticalcorrelation.
 4. A circuit for separating the luminance and chrominancesignals from a video signal as recited in claim 3 whereinthe luminanceand chrominance signal separating means include a frame memory, anadder, a subtracter, and wherein the video signal is supplied in commonto the adder, the subtracter, and the frame memory and the output of theframe memory is supplied in common to the adder and the subtracterwhereby the luminance signal is derived at the output of the adder andthe chrominance signal is derived at the output of the subtracter basedon frame correlation.
 5. A circuit for separating the luminance andchrominance signals from a video signal as recited in claims 1, 2, 3, or4 wherein each intermediate value selecting means comprises a maximumvalue circuit, a minimum value circuit, a first adder, a second adderand a subtracter and wherein each of the outputs of the luminance or thechrominance signal separating means is input in common to the maximumvalue circuit, the minimum value circuit, and the first adder, theoutput of the maximum value circuit and minimum value circuits are addedtogether by the second adder, and the output of the second adder issubtracted by the subtracter from the output of the first adder toproduce an output which is a separated luminance or chrominance signalhaving an intermediate value.
 6. A circuit for separating the luminanceand chrominance signals from a video signal as recited in claim 1wherein each intermediate value selecting means comprises a plurality ofN maximum value selecting circuits, where N is the number of luminanceor chrominance signal separating means, and a minimum value circuit, andwherein the output of each luminance or chrominance signal separatingmeans is input to N-1 of the maximum value selecting circuits so thateach maximum value circuit has N-1 inputs, and the outputs of themaximum value circuits are input to the minimum value circuit wherebythe output of the minimum value circuit is an intermediate one of theseparated luminance or chrominance signals, respectively.
 7. A circuitfor separating the luminance and chrominance signals from a video signalas recited in claim 1 wherein each intermediate value selecting meanscomprises a plurality of N minimum value selecting circuits, where N isthe number of luminance or chrominance signal separating means, and amaximum value circuit, and wherein the output of each luminance orchrominance signal separating means is input to N-1 of the minimum valueselecting circuits so that each minimum value circuit has N-1 inputs,and the outputs of the minimum value circuits are input to the maximumvalue circuit whereby the output of the maximum value circuit is anintermediate one of the separated luminance or chrominance signals,respectively.
 8. A circuit for separating the luminance and chrominancesignals from a video signal as recited in claims 6 or 7 wherein thenumber N of luminance and chrominance signal separating means is threeand the luminance and chrominance signal separating means utilizehorizontal, vertical and frame correlation, respectively.
 9. A circuitfor separating the luminance and chrominance signals from a video signalas recited in claim 1 wherein the luminance and chrominance signalseparating means includes a transversal filter for signal separationusing the horizontal correlation.